It is a common practice for motor vehicles to be equipped with independent suspension systems for absorbing road shock and other vibrations while providing a smooth and comfortable ride for the vehicle occupants. In suspension systems of this type, a stabilizer bar is often used to increase the roll rigidity and improve the steering stability of the vehicle. Typically, the stabilizer bar is a rod-shaped member having an elongated central segment oriented to extend laterally across the vehicle and an arm segment extending longitudinally at each end of the central segment to form a generally U-shaped configuration. The central segment of the stabilizer bar is supported for rotation about its own longitudinal axis by one or more mounting brackets which are fixed to the vehicle body or frame. Most commonly, the mounting brackets are positioned in close proximity to the arm segments for minimizing any bending moments which may be induced into the stabilizer bar. The distal end of each arm segment is coupled to a control arm of the suspension system by an end link. When the vehicle is subjected to a lateral rolling force such as, for example, while the vehicle negotiates a turn, the arm segments pivot in opposite directions with respect to the longitudinal axis of the central segment. As a result, torsional reaction forces are generated which act through the arm segments to urge the control arms to move toward their normal position. Thus, the vehicle body will be prevented from excessive rolling or leaning to either side by the torsional resistance produced by the stabilizer bar.
In response to the recent increase in consumer demand for sport-utility and performance vehicles which are typically equipped with sport-type independent suspension systems, automotive suspension designers have traditionally increased the diameter of the stabilizer bar to provide a commensurate increase in roll stiffness. Unfortunately, increasing the diameter of the stabilizer bar can also compromise the ride quality of the vehicle by making the ride feel harsher during normal driving conditions. Moreover, increasing the diameter of the stabilizer bar will also add weight and cost to the vehicle. Other design modifications which can be incorporated into the suspension system to reduce cornering roll of the vehicle body include increasing the spring rate or stiffness of the suspension springs and/or modifying the shock absorber damping characteristics. As before, these modifications can also result in a compromised ride quality by transmitting more road vibration to the vehicle and providing a harsher feel to the vehicle occupants when the vehicle is driven over small bumps or potholes in the road surface.
As noted, each end of the stabilizer bar is typically attached to a corresponding control arm by an end link. FIG. 1, shows a conventional or prior art end link which is similar in construction to that shown in U.S. Pat. No. 4,875,703 to Murakami. Specifically, end link 10 is composed of a bolt 12 onto which is placed a first washer 14a and a first rubber bushing 16a. Bolt 12 is then passed through a hole 18 provided in a flattened end 20 of an arm segment 22 of a stabilizer bar 24. Thereafter, a second rubber bushing 16b and second washer 14b are placed over bolt 12 as shown. Next, a rigid cylindrical spacer 26 is placed over bolt 12 as are a third washer 14c and a third bushing 16c. Bolt 12 then passes through a bore 28 formed in a control arm of the suspension system which, in the present example, is a bracket 30 attached to or integrally formed as part of an upper control arm 32. A fourth rubber bushing 16d and a fourth washer 14d are then placed over bolt 12 and a nut 34 is fastened to the end of bolt 12 to secure the assembly together. Rubber bushings 14a through 14d are provided to allow control arm 30 and arm segment 22 of stabilizer bar 24 to pivot relative to one another as the suspension travels through its range of motion. This pivoting action, typically referred to as angularity, is caused by the fact that control arm 30 pivots in a plane which is substantially perpendicular to the plane through which arm segment 22 of stabilizer bar 24 pivots. Several variations of the prior art end link just described have been disclosed in U.S. Pat. Nos. 4,875,703; 4,944,523; 5,449,193; and 5,551,722.
One disadvantage of the system just described is that the rubber bushings, while necessary to allow for angularity, reduce the initial effectiveness of the stabilizer bar. In fact, the stabilizer bar does not begin to experience torsional forces and act to correct the roll condition of the vehicle until the rubber bushings have been substantially compressed and, in affect, have become solid members. This initial lack of stabilizing action allows the vehicle to gain momentum in the roll direction. This momentum must be overcome by the torsional forces of the stabilizer bar in addition to the forces which are imparted by the cornering action. Thus, this initial "softness" in roll rigidity often gives the driver a perception that the vehicle is not properly responding to the steering input. While various shapes and stiffness for the rubber bushings have been developed over the years to minimize this affect, a limiting design constraint is that the system must remain pliable enough to accommodate the angularity between the stabilizer bar and the suspension control arm.